The present invention relates to an article gripping apparatus used for gripping and conveying an article with fingers of a robot or an automatic assembly system and, more particularly, to an article gripping apparatus suitable for gripping an optical lens used in optical equipment.
Conventionally, various types of article gripping apparatus for gripping and conveying an article as described below are known.
(i) An article gripping apparatus, utilizing a so-called chucking operation, grips an article by drawing and holding the article by a suction force such as vacuum suction, and conveys the gripped article from a predetermined position to another position or assembles it in another article. An article gripping apparatus of this type is disclosed in Japanese Utility Model Publication No. 54-6949, Japanese Patent Laid-Open (Kokai) No. 55-150989, Japanese Patent Publication Nos. 61-35089 and 62-18317, and the like. These specifications disclose article gripping apparatuses which directly chuck and hold the article.
(ii) Another known article gripping apparatus employs a method of gripping an article using a plurality of gripping members or finger members. For example, Japanese Utility Model Publication No. 56-6315 discloses an apparatus wherein three pawls are coupled to a motor through coupling means constituted by a threaded shaft and a bevel gear, and are opened/closed by the motor to grip an article Japanese Patent Publication No. 58-50835 discloses an apparatus wherein three finger members are driven by a motor through gears.
(iii) Various functions of a gripping apparatus of the present invention include a function of centering an article to be gripped. An article gripping apparatus comprising a centering function is disclosed in, e.g., Japanese Patent Laid-Open (Kokai) No. 61-256004.
(iv) Furthermore, Japanese Patent Laid-Open (Kokai) No. 63-14500 discloses a conventional mounting head comprising a suction nozzle and a position regulating pawl for regulating the position of an article.
As described above, the present invention particularly relates to an article gripping apparatus suitable for gripping an optical lens used in optical equipment. A lens surface of such an optical lens is required to have high surface finishing precision and cleanliness in order to transmit and refract a light beam. As a result, when the optical lens is assembled in a lens barrel or optical equipment, an optical functional surface of the lens must be free from damage or contamination due to direct contact with the optical functional surface upon gripping of the optical lens.
For this reason, when the optical lens is assembled in the lens barrel, it is impossible to grip an outer peripheral portion of the optical lens from the outside using finger members so as to fit it into the lens barrel. More specifically, the inner peripheral surface of the lens barrel and the outer peripheral surface of the optical lens have substantially the same diameters. Therefore, there is no allowance for gripping the outer peripheral portion of the optical lens from the outside by the finger members. As a result, it is impossible to fit the optical lens into a predetermined position of the lens barrel while gripping the optical lens.
After the optical lens is fitted in a lens locking portion inside the lens barrel, a metal elastic ring or C-ring for fixing the optical lens in position must be inserted in the lens barrel. Thus, in the gripping apparatus used for inserting these rings into the lens barrel, the ring is gripped by a plurality of finger members from a radially outer position, and is pressed radially inwardly so as to decrease an interval between these finger members, and reduce the outer diameter of the ring in a natural state. In this state, the ring is inserted in the lens barrel in which the optical lens was fitted. In this gripping apparatus, since a pressing force is applied to the ring by the finger members, it is difficult to remove the ring from the gripping apparatus. In this manner, if the ring cannot be smoothly removed from the gripping apparatus, lens fixing by the ring cannot be reliably performed, thus posing a problem.